C. Prominent horizontal fissure  

On chest X-ray, transient tachypnoea of the newborn is typified by interstitial pulmonary oedema with fluid tracking into, and therefore outlining, the interlobar (especially horizontal) fissure, producing a conspicuously thickened fissure sign; low lung volumes, reticulogranular pattern, and air bronchograms are hallmarks of hyaline-membrane disease, not TTN [Ponhold, 1981, PMID 7302476].